The ecology and epidemiology of arboviruses in South Africa with reference to their anthropod vectors

Abstract:

By definition an arthropod-borne virus (arbovirus) is a virus transmitted biologically between vertebrate hosts by an arthropod vector. It multiplies in both the vertebrate and arthropod host and requires both types of host for its perpetuation. The vector acquires virus by feeding on a viraemic vertebrate, the virus then multiplies in the vector, including the salivary glands, and after an interval is transmitted to another vertebrate when a second blood meal is taken. <br><br> As medical entomologist to the Arbovirus Unit of the National Institute for Virology (formerly a laboratory of the South African Institute for Medical Research), I have undertaken research on the ecology and epidemiology of the arboviruses in South Africa since 1964. I am interested in this topic with particular reference to the arthropod vectors which are responsible for transmitting these viruses, both in maintenance cycles with wild vertebrates and carrying virus over to man to cause outbreaks of disease. The published papers included in the present compilation relate mainly to 5 arboviruses which are of significant medical importance. These viruses are the following: West Nile (WN) virus: Flaviviridae, Flavivirus Sindbis (SIN) virus: Togaviridae, Alphavirus Chikungunya (CHIK) virus: Togaviridae, Alphavirus Rift Valley fever (RVF) virus: Bunyaviridae, Phlebovirus Dengue (DEN) virus: Flaviridae, Flavivirus <br><br> They are all mosquito-borne viruses and 48 of the total 65 papers included relate to them. There are also 7 papers on miscellaneous arboviruses including tick-borne arboviruses. Hepatitis B virus (HBV) (Hepadnaviridae; Hepadnavirus) receives attention and, although it does not fit the definition of an arbovirus, observations on field and laboratory bedbugs and tampan ticks suggested they could be mechanical vectors so this work is included (8 papers). Finally, the possibility that Human Immunodeficiency virus (HIV) (Retroviridae, Retrovirus) might be transmitted by insects has also been tested experimentally (2 papers). <br><br> The largest number of papers (22) relate to vectors of WN and SIN viruses (section 1). The papers in this section are divided into 4 subsections: field epidemiology, laboratory vector competence experiments, mosquito ecology and lastly mosquito taxonomy and distribution. The papers in the other 5 sections are not so divided, although on the whole the same topics are considered. Information is needed on all these topics if a full picture of the ecology and epidemiology of the virus in question is to be built up. The "coordinating document" which follows below give a summary of the scope of the work represented by the 65 papers and includes a summary of the main results and conclusions for each publication or group of publications.<br><br> The title of the proposed D.Sc. limits the study to South Africa. There are, however, 3 papers relating to work on vectors that occur outside South Africa which are included. These are one on the taxonomy and distribution of the Culex univittatus group of mosquitoes in Madagascar and 2 papers on the tampan tick as a vector of HBV in Namibia. I consider it important to include these 2 pieces of work as they make interesting comparisons with the work on the Culex univittatus group and the project on Cimex lectularius and HBV in South Africa respectively.